Chip packaging process

ABSTRACT

A chip packaging process is provided. First, a cavity is formed on a heat sink. A first encapsulant is formed on the bottom of the cavity. A circuit substrate is disposed over the heat sink. The circuit substrate has an opening that corresponds in position to the cavity. Thereafter, a chip is disposed on the first encapsulant and the chip is electrically connected to the circuit substrate. Finally, a compound is deposited over the first encapsulant and the chip to form a chip package. The chip package is warp resistant and the chip packaging process increases overall production yield.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of an application Ser. No. 10/907,340, filed on Mar. 30, 2005, now allowed, which claims the priority benefit of Taiwan application serial no. 93109186, filed on Apr. 2, 2004. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a chip package structure and a chip packaging process. More particularly, the present invention relates to a warp-resistant chip package structure and chip packaging process for improving the yield of production.

2. Description of the Related Art

With the rapid progress in electronic technologies and semiconductor manufacturing in recent years, a lot of personalized and multifunctional electronic products flooded the market. Moreover, these electronic products are often miniaturized and downsized for portability. In the area of semiconductor production, the fabrication of integrated circuits (IC) can be roughly divided into three main stages: integrated circuit design, integrated circuit fabrication and integrated circuit packaging. In general, raw chips are produced after going through a series of steps including wafer production, circuit design, mask production and wafer dicing operation. Each piece of raw chip cut out from the wafer must be electrically connected to a substrate for external communication through the bonding pads thereon. Moreover, each raw chip must be encapsulated by an encapsulant to form an IC package that prevents moisture, heat or electrical noise from interfering with its function and a medium for connecting with an external circuit such as a printed circuit board (PCB) or other packaging substrate.

Due to the rapid advance in IC production technologies, the operating speed of each chip continues to increase so that various types of digital data processing and computation are increasingly efficient. However, as the level of integration of circuits within each chip increases exponentially, the amount of heat generated per unit area in normal operation also increases accordingly. At maximum operating speed, the need to dissipate the heat away from the chip fast enough is critical. Conventionally, a metallic heat sink with high heat-dissipating capacity is disposed on a chip package to absorb heat and conduct the heat away to the surrounding atmosphere.

FIG. 1 is a schematic cross-sectional view showing the structure of a conventional chip package. As shown in FIG. 1, the chip package structure 100 comprises a chip 110, a circuit substrate 120, a heat sink 130 and an encapsulant 140. The circuit substrate 120 having an opening 120 a therein is disposed on the heat sink 130. The back surface 110 b of the chip 110 is mounted to the heat sink 130 within the opening 120 a of the circuit substrate 120 by adhesive glue (not shown). The active surface 110 a of the chip 110 has a plurality of bonding pads 112 thereon. The circuit substrate 120 has a plurality of first bonding pads 122 a and a plurality of second bonding pads 122 b surrounding the first bonding pads 122 a. The chip 110 and the circuit board 120 are electrically connected through a wire-bonding process. Typically, each bonding pad 112 on the chip 110 is electrically connected to a corresponding first bonding pad 122 a on the circuit substrate 120 through a conductive wire 150.

As shown in FIG. 1, the encapsulant 140 fills up the opening 120 a entirely and encapsulates the chip 110, the conductive wires 150 and the first bonding pads 122 a on the circuit substrate 120. The encapsulant 140 prevents moisture, heat or electrical noise from affecting the chip 110 and protects the conductive wires 150 against mechanical damage. Furthermore, a plurality of conductive bumps 160 is formed on the second bonding pads 122 b of the circuit substrate 120 to serve as a medium of contact for connecting the chip package 100 to external circuits.

To form the encapsulant in the aforementioned chip packaging process, a molding compound such as epoxy resin is heated to a semi-liquid form at a high temperature and injected into a mold. Thereafter, the molding compound is cooled to form a solidified encapsulant. However, the heat sink and the encapsulant have different coefficient of thermal expansion (CTE). Thus, a thermal stress of non-uniform magnitude is often generated inside the chip package somewhere between the heat sink and the encapsulant during the cooling process. Due to the thermal stress, the chip package is more likely to warp or crack. The warping or cracking of the chip package frequently leads to irreversible damage to either the chip or the conductive wires. Therefore, the yield of the chip packaging process can not be enhanced effectively.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to provide a chip package structure, wherein the thermal stress around a chip is uniform. Thus, warping and cracking of the chip package is significantly reduced and the reliability of the connection between the chip and conductive wires inside the chip package is maintained.

The prevent invention is further directed to provide a chip packaging process that includes the step of encapsulating a chip with an identical material so that the effect of thermal stress on the chip package is substantially reduced. Consequently, there is a significant improvement in overall product yield of the chip package.

According to an embodiment of the present invention, a chip package structure is provided. The chip package comprises a heat sink, a circuit substrate, a chip, a first encapsulant, a second encapsulant and a plurality of conductive bumps. The heat sink has a cavity and the circuit substrate is disposed on the heat sink. The circuit substrate has a top surface and an opening that corresponds in position to the cavity. The chip is disposed at the bottom of the cavity and is electrically connected to the circuit substrate. The first encapsulant is disposed between the heat sink and the chip. Furthermore, the first encapsulant is in contact with the sidewall of the cavity. The second encapsulant is disposed over the first encapsulant to cover the chip and a portion of the circuit substrate. The conductive bumps are disposed on the top surface of the circuit substrate outside the second encapsulant to serve as a medium of contact for connecting the chip package with external circuits.

In an embodiment of the present invention, the first encapsulant has a height small than, equal to or greater than the depth of the cavity. The chip package structure may further comprise a heat-conductive interlayer such as a metallic layer or a patterned metallic layer. The heat-conductive interlayer is disposed between the chip and the first encapsulant and extends between the circuit substrate and the heat sink to conduct heat directly away to the heat sink. The chip and the circuit substrate are electrically connected through a plurality of conductive wires bonded to the circuit substrate and the chip in a wire-bonding process. The second encapsulant further encapsulates the conductive wires to protect the conductive wires against possible damage resulting from external forces.

In one embodiment of the present invention, the first encapsulant and the second encapsulant are fabricated using an identical material such as epoxy resin. In addition, the conductive bumps are distributed around the second encapsulant.

The present invention further provides an alternative chip package structure. The chip package comprises a heat sink, a circuit substrate, a chip, an encapsulant and a plurality of conductive bumps. The heat sink has a cavity and the circuit board is disposed on the heat sink. The circuit board has a top surface and an opening that corresponds in position to the cavity. The chip is disposed in the cavity. The chip and the circuit substrate are electrically connected through a plurality of conductive wires. The encapsulant encapsulates the chip and the conductive wires and is in contact with the sidewalls and bottom surface of the cavity. The conductive bumps are disposed on the top surface of the circuit substrate.

The present invention further provides a chip packaging process comprising the following steps. First, a cavity is formed on a heat sink and then a first encapsulant is formed at the bottom of the cavity. A circuit substrate is disposed on the heat sink. The circuit substrate has an opening that corresponds in position to the cavity. A chip is disposed on the first encapsulant. The chip and the circuit substrate are electrically connected. Thereafter, a second encapsulant is formed over the first encapsulant to encapsulate the chip and a portion of the circuit substrate. Ultimately, a plurality of conductive bumps are formed on the circuit substrate.

In one embodiment of the present invention, the chip packaging process may include forming a heat-conductive interlayer over the first encapsulant and the heat sink before disposing the circuit substrate over the heat sink. Thus, a more efficient heat conductive path is created. In addition, the heat-conductive interlayer can be a metallic layer or a patterned metallic layer. Moreover, the chip and the circuit substrate are electrically connected through conductive wires formed in a wire-bonding process.

In brief, the chip package structure and the chip packaging process is characterized by disposing a first encapsulant between the chip and the heat sink to increase the gap formed between the chip and the heat sink. The first encapsulant and the second encapsulant are fabricated from an identical material so that they have an identical coefficient of thermal expansion. Hence, the degree of warping in the chip package is minimized when the molding compound for forming the second encapsulant is cooled. Furthermore, since the chip is entirely encapsulated by the first encapsulant and the second encapsulant, a uniform thermal stress is generated around the chip. As a result, reliability of the connection between the chip and the conductive wires is maintained and the chip packaging process with a higher overall yield is provided.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a schematic cross-sectional view showing the structure of a conventional chip package.

FIGS. 2A through 2G are schematic cross-sectional view showing the steps in a chip packaging process for producing a chip package according to a first embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of a second chip package structure fabricated using the chip packaging process according to the first embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of a third chip package structure fabricated using the chip packaging process according to the first embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view of a first chip package structure according to a second embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view of a second chip package structure according to the second embodiment of the present invention.

FIGS. 7A and 7B are graphs obtained from a simulation showing the degree of warping between the chip package of the present invention and the conventional chip package at different temperatures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

FIGS. 2A through 2G are schematic cross-sectional view showing the steps in a chip packaging process for producing a chip package according to a first embodiment of the present invention. First, as shown in FIG. 2A, a cavity 230 a is formed on a heat sink 230. The cavity 230 a is formed, for example, by performing mechanical drilling, laser drilling or etching. As shown in FIG. 2B, a first encapsulant 240 a is formed on the bottom of the cavity 230 a by applying a material such as epoxy resin. Thereafter, as shown in FIG. 2C, a circuit substrate 220 is disposed on the heat sink 230. The circuit substrate 220 has an opening 220 a that corresponds in position to the cavity 230 a. Furthermore, the circuit substrate 220 has a top surface 224 a having a plurality of first bonding pads 222 a and a plurality of second bonding pads 222 b thereon. The second bonding pads 222 b are located around the first bonding pads 222 a. The bottom surface 224 b of the circuit substrate 220 is attached to the heat sink 230 by adhesive glue (not shown), for example.

As shown in FIG. 2D, a chip 210 is disposed on the first encapsulant 240 a. The chip 210 has an active surface 210 a and a back surface 210 b. The active surface 210 a has a plurality of bonding pads 212 thereon. As shown in FIG. 2E, a wire-bonding process is performed to electrically connect the bonding pads 212 on the chip 210 with the first bonding pads 222 a on the circuit substrate 220 by a plurality of conductive wires 250. As shown in FIG. 2F, a second encapsulant 240 b is formed over the first encapsulant 240 a. The second encapsulant 240 b is fabricated from a material identical to the first encapsulant 240 a (such as epoxy resin). The second encapsulant 240 b encapsulates the first bonding pads 222 a, the conductive lines 250 and the chip 210 (including the bonding pads 212). Finally, as shown in FIG. 2G, a plurality of conductive bumps 260 are formed on the second bonding pads 222 b of the circuit substrate 220. After the conductive bumps 260 are formed, a complete chip package 200 is provided. The conductive bumps 260 has a height greater than the height of the second encapsulant 240 b above the top surface 224 a of the circuit substrate 220 to facilitate electrically connecting the chip package 200 through the conductive bumps 260 with an external device.

In the present embodiment, the chip package structure and the chip packaging process use identical material (including the second encapsulant 240 b and the first encapsulant 240 a) to encapsulate the chip. The material around the chip serves as a buffer to reduce the degree of warping in the chip package, maintains a fixed relationship between the chip and the conductive wires and increases product yield of the chip packaging process. However, the chip packaging process of the present invention further permits the disposition of the circuit substrate 220 over the heat sink 230 before forming the first encapsulant 240 a inside the cavity 230 a for supporting the chip 210. Since the process has been explained with reference to FIGS. 2B and 2C, detailed description is omitted.

In addition, both the first encapsulant 240 a and the second encapsulant 240 b may be fabricated from an identical material as shown in FIG. 2G. Furthermore, since the chip 210 may be located close to the center of the cavity 230 a when the height H1 of the first encapsulant 240 a and the height H2 of the second encapsulant 210 b are near, a uniform stress around the chip 210 is obtained. In other words, the chip 210 is more resistance to warping as a result of thermal stresses. However, the height H1 of the first encapsulant 240 a need not be close to the heights H2 of the second encapsulant 230 b as shown in FIG. 2G. In practice, different types of molding compounds can be used to match the particular type of design to reduce production cost.

FIG. 3 is a schematic cross-sectional view of another chip package structure fabricated using the chip packaging process according to the first embodiment of the present invention. As shown in FIG. 3, the top surface of the first encapsulant 240 a is at a level lower than the bottom surface 224 b of the circuit substrate 220. FIG. 4 is a schematic cross-sectional view of still another chip package structure fabricated using the chip packaging process according to the first embodiment of the present invention. As shown in FIG. 4, the circuit substrate 220 is formed over the heat sink before forming the first encapsulant 240 a so that the top surface of the first encapsulant 240 a can reach a height between the top surface 224 a and the bottom surface 224 b of the circuit substrate 220.

Using the first type of chip package structure and its corresponding chip packaging process as a base, a chip package structure and chip packaging process having a higher heat dissipation can be produced. FIG. 5 is a schematic cross-sectional view of a first chip package structure according to a second embodiment of the present invention. As shown in FIGS. 2G and 5, the chip package structure 300 in FIG. 5 has an additional heat-conductive interlayer 270 disposed between the chip 210 and the first encapsulant 240 a. The heat-conductive interlayer 270 is fabricated by silver, copper or some other heat conductive metallic materials. Furthermore, the heat-dissipation layer 270 may extend between the circuit substrate 220 and the heat sink 230 so that heat generated by the chip 210 can be directly transferred to the heat sink 230 via the heat-conductive interlayer 270.

The chip packaging process for forming the chip package structure 300 in FIG. 5 includes performing an electroplating to form the heat-conductive interlayer 270 after forming the first encapsulant 240 a (as shown in FIG. 2B). The process may also include a patterning step to form a patterned heat-conductive interlayer 270. FIG. 6 is a schematic cross-sectional view of a second chip package structure according to the second embodiment of the present invention. As shown in FIG. 6, the top surface of the first encapsulant is at a level lower than the bottom surface 224 b of the circuit substrate 220. The heat-conductive interlayer 270 is located on the top surface of the first encapsulant 240 a, a portion of the sidewalls of the cavity 230 a and between the heat sink 230 and the circuit substrate 220.

FIGS. 7A and 7B are graphs obtained from a simulation showing the degree of warping between the chip package of the present invention and the conventional chip package at different temperatures. The simulated temperature is −65° C. in FIG. 7A and the simulated temperature is 225° C. in FIG. 7B. In addition, the curve 710 represents the warping of the diagonal line in a conventional chip package. Similarly, the curve 720 represents the warping of the diagonal line in the chip package structure shown in FIG. 2G and the curve 730 represents the warping of the diagonal line in the chip package structure shown in FIG. 5. As shown in FIGS. 7A and 7B, there are substantial improvements in the degree of warping for the chip package structure fabricated according to the present invention.

In summary, the main idea behind the chip package structure and the chip packaging process is to form a cavity on a heat sink, depositing a material into the cavity to form a first encapsulant and disposing a chip over the first encapsulant. The first encapsulant serves to increase the gap formed between the chip and the heat sink. Thereafter, the encapsulating material is deposited to form a second encapsulant that encapsulates the chip. The first encapsulant and the second encapsulant are fabricated from an identical material such as epoxy resin so that they have an identical coefficient of thermal expansion. Hence, the degree of warping in the chip package is minimized when the second encapsulant is cooled. Furthermore, since the chip is entirely encapsulated by the first encapsulant and the second encapsulant, a uniform thermal stress is generated around the chip. As a result, the chip and the conductive wires are able to remain in a fixed location and provide the chip packaging process with a higher overall yield.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents. 

1. A chip packaging process, comprising: forming a cavity on a heat sink; forming a first encapsulant at the bottom of the cavity, wherein the first encapsulant is in contact with sidewalls of the cavity; disposing a circuit substrate on the heat sink, wherein the circuit substrate has an opening that corresponds in position to the cavity; disposing a chip on the first encapsulant; electrically connecting the chip and the circuit substrate; forming a second encapsulant over the first encapsulant to encapsulate the chip and a portion of the circuit substrate; and forming a plurality of conductive bumps on the circuit substrate.
 2. The chip packaging process of claim 1, further comprising forming a heat-conductive interlayer over the first encapsulant and the heat sink before disposing the chip.
 3. The chip packaging process of claim 2, wherein the heat-conductive interlayer is a metallic layer.
 4. The chip packaging process of claim 2, wherein the heat-conductive interlayer is a patterned metallic layer.
 5. The chip packaging process of claim 1, wherein the step of electrically connecting the chip and the circuit substrate comprises performing a wire-bonding process.
 6. A chip packaging process, comprising: forming a cavity on a heat sink; forming a first encapsulant at the bottom of the cavity; disposing a circuit substrate on the heat sink, wherein the circuit substrate has an opening that corresponds in position to the cavity; disposing a chip on the first encapsulant; electrically connecting the chip and the circuit substrate; forming a second encapsulant over the first encapsulant to encapsulate the chip and a portion of the circuit substrate; forming a plurality of conductive bumps on the circuit substrate; and forming a heat-conductive interlayer over the first encapsulant and the heat sink before disposing the chip.
 7. The chip packaging process of claim 6, wherein the heat-conductive interlayer is a metallic layer.
 8. The chip packaging process of claim 6, wherein the heat-conductive interlayer is a patterned metallic layer. 